DOC: Update docstrings of np.sum and np.prod.
DOC: Update docstrings of np.sum and np.prod.

* Improved language of sum doc for axis subheading. Added clarification
  of important axis values--{0,1}->iterative {row,column} sum.

* Improved language of product axis subheading.

numpy/numpy,gmcastil/numpy,pizzathief/numpy,b-carter/numpy,anntzer/numpy,dwillmer/numpy,WarrenWeckesser/numpy,chiffa/numpy,endolith/numpy,tacaswell/numpy,seberg/numpy,chatcannon/numpy,behzadnouri/numpy,grlee77/numpy,kiwifb/numpy,mwiebe/numpy,rgommers/numpy,behzadnouri/numpy,simongibbons/numpy,anntzer/numpy,shoyer/numpy,anntzer/numpy,maniteja123/numpy,mhvk/numpy,chatcannon/numpy,Eric89GXL/numpy,tacaswell/numpy,AustereCuriosity/numpy,simongibbons/numpy,pbrod/numpy,simongibbons/numpy,bertrand-l/numpy,seberg/numpy,dwillmer/numpy,endolith/numpy,Eric89GXL/numpy,ESSS/numpy,solarjoe/numpy,numpy/numpy,kiwifb/numpy,rherault-insa/numpy,kiwifb/numpy,solarjoe/numpy,stuarteberg/numpy,MSeifert04/numpy,WarrenWeckesser/numpy,abalkin/numpy,ahaldane/numpy,chiffa/numpy,numpy/numpy,rherault-insa/numpy,njase/numpy,madphysicist/numpy,shoyer/numpy,gmcastil/numpy,pizzathief/numpy,nbeaver/numpy,grlee77/numpy,joferkington/numpy,grlee77/numpy,abalkin/numpy,jakirkham/numpy,maniteja123/numpy,pbrod/numpy,ContinuumIO/numpy,mattip/numpy,ahaldane/numpy,mhvk/numpy,tacaswell/numpy,gmcastil/numpy,utke1/numpy,MSeifert04/numpy,tynn/numpy,behzadnouri/numpy,pizzathief/numpy,mhvk/numpy,tynn/numpy,argriffing/numpy,rgommers/numpy,nbeaver/numpy,madphysicist/numpy,Dapid/numpy,gfyoung/numpy,ddasilva/numpy,pizzathief/numpy,WarrenWeckesser/numpy,pbrod/numpy,njase/numpy,ContinuumIO/numpy,drasmuss/numpy,skwbc/numpy,SiccarPoint/numpy,bringingheavendown/numpy,MSeifert04/numpy,shoyer/numpy,pizzathief/numpy,rherault-insa/numpy,jonathanunderwood/numpy,madphysicist/numpy,WarrenWeckesser/numpy,chiffa/numpy,pdebuyl/numpy,ahaldane/numpy,chatcannon/numpy,jakirkham/numpy,drasmuss/numpy,jorisvandenbossche/numpy,jorisvandenbossche/numpy,bertrand-l/numpy,nbeaver/numpy,gfyoung/numpy,jakirkham/numpy,MSeifert04/numpy,madphysicist/numpy,skwbc/numpy,grlee77/numpy,jakirkham/numpy,ESSS/numpy,ahaldane/numpy,skwbc/numpy,Dapid/numpy,charris/numpy,simongibbons/numpy,pbrod/numpy,jonathanunderwood/numpy,AustereCuriosity/numpy,dwillmer/numpy,SiccarPoint/numpy,rgommers/numpy,argriffing/numpy,argriffing/numpy,drasmuss/numpy,abalkin/numpy,shoyer/numpy,joferkington/numpy,charris/numpy,b-carter/numpy,grlee77/numpy,bertrand-l/numpy,jakirkham/numpy,madphysicist/numpy,charris/numpy,mattip/numpy,WarrenWeckesser/numpy,stuarteberg/numpy,maniteja123/numpy,rgommers/numpy,ddasilva/numpy,jorisvandenbossche/numpy,seberg/numpy,ssanderson/numpy,shoyer/numpy,joferkington/numpy,ssanderson/numpy,utke1/numpy,jorisvandenbossche/numpy,utke1/numpy,simongibbons/numpy,mhvk/numpy,pdebuyl/numpy,joferkington/numpy,AustereCuriosity/numpy,bringingheavendown/numpy,seberg/numpy,stuarteberg/numpy,numpy/numpy,ESSS/numpy,endolith/numpy,pdebuyl/numpy,jorisvandenbossche/numpy,ContinuumIO/numpy,SiccarPoint/numpy,mattip/numpy,MSeifert04/numpy,Eric89GXL/numpy,endolith/numpy,b-carter/numpy,mwiebe/numpy,mattip/numpy,Eric89GXL/numpy,mwiebe/numpy,tynn/numpy,mhvk/numpy,njase/numpy,gfyoung/numpy,ddasilva/numpy,anntzer/numpy,Dapid/numpy,jonathanunderwood/numpy,ahaldane/numpy,bringingheavendown/numpy,pdebuyl/numpy,solarjoe/numpy,dwillmer/numpy,SiccarPoint/numpy,charris/numpy,ssanderson/numpy,pbrod/numpy,stuarteberg/numpy